Nylon flat and bulky continuous filament yarns have many desirable properties. However, the nylon continuous filament yarns in widespread commercial use are almost exclusively solid filament yarns with no interior voids. Yarns containing hollow filaments, i.e., filaments that have at least one longitudinal void, can provide fabrics which are lighter in weight but provide the same cover (fabric opacity) and enhanced heat retention as heavier weight conventional fabrics, i.e., higher heat retention determined as CLO values. In addition, these flat filament yarns can provide a distinctive luster in fabric and when textured can provide cotton-like fabric aesthetics. However, hollow filaments having sufficient mechanical quality for end-use processing without broken filaments is required for successful use in downstream textile processing, such as texturing (if a bulky yarn is desired), slashing, warping, beaming, knitting, weaving, dyeing and finishing. Poor mechanical quality can lead to filament fracture and/or filament fibrillation which may be undesired during initial end-use processing; but may be desirable during such fabric finishing processes, as brushing and sanding to provide suede-like fabric surfaces. A balance between mechanical quality for processing into fabrics prior to finishing of the fabric surfaces, high void content for reduced fabric weight and other features, such as dye uniformity, are required for hollow filament yarns to be commercially useful. It is also important for some critical nylon end-uses to maintain physical uniformity, both along-end and between the various filaments, because such non-uniformity often shows up in the eventual dyed fabrics as dyeing defects and/or as broken filaments after textile end-use processing.
Processes are known for producing nylon hollow filaments; however, such processes are typically low speed spinning processes which require a separate (split) or in-line (coupled) drawing step with a high process draw ratio (PDR). In a coupled spin/draw process the speed of the yarn entering the draw zone (feed roll speed) is typically less than 1000 meters per minute (mpm) and such processes therefore have low spinning productivity (P.sub.S), and further, such known processes for making hollow filaments have not been able to provide the desired combination of mechanical quality, void content, and/or dye uniformity.